1. Field of Invention
The present invention relates to a light control member provided with a light input face for introducing light from a light source and a light output face for emitting the light, and to a surface light source device employing the light control member and to a display (such as LCD) provided with a displaying member (such as LCD panel) backlighted by the surface light source device.
2. Related Art
A LCD display a LCD of which is backlighted by a surface light source device is known well, being broadly applied to monitor displays for personal computers, television sets and others.
In general, a surface light source device has a light source called “primary light source”. A known type of surface light source device for backlighting applied to such uses is called “directly-under-type surface light source device”.
A directly-under-type surface light source device has a primary light source which is disposed behind (directly under) a displaying member (such as LCD panel). Accordingly, it is required to prevent the primary light source looks conspicuous through the displaying member. In other words, an image of the primary light source must to be blurred. For this purpose, employed is an optical member diverging travelling directions of the light emitted from the primary light source, typically a diffusing member having a high light diffusing ability.
However, an excessive high light diffusing ability brings backlight by light like a rather completely diffused light, resulting in a reduced frontal brightness. Then it is needless to say that a weak light diffusing ability fails to blur the image of primary light source, resulting in a reduced display quality.
FIG. 20 illustrates an example of prior art (first prior art) for relaxing such a problem, which is disclosed in Document 1 noted below. Referring to FIG. 20, surface light source device 100 has light source (primary light source) 101, reflection member 102, diffusion sheet 103and polygon-pyramids-sheet 104.
Light of light source (primary light source) 101 is inputted to polygon-pyramids-sheet 104 via diffusion sheet 103 after or without being reflected by reflection member 102, then being outputted from an opposite face (light output face) of the polygon-pyramids-sheet. Travelling directions of light are diverged by diffusion sheet 103 and gathered around a frontal direction (normal direction). As a result, a relaxed falling of brightness as viewed from the frontal direction is obtained.
FIG. 21 illustrates another example of prior art (second prior art), which is disclosed in Document 2 noted below. Referring to FIG. 21, surface light source device 110 has light source (primary light source) 111, reflection member 112, multiprism-sheet 113 and dark-area-removing-sheet 114.
Light of light source (primary light source) 111 is outputted as an illumination light via multiprism-sheet 113 and dark-area-removing-sheet 114. The outputted illumination light irradiates, for instance, a LCD panel.                Document 1; Tokkai-Hei 6-265888        Document 2; Tokkai-Hei 3-200930        
However, the first embodiment is subject to a fact that light from light source 101 include a light component which is incident to a lower face of polygon-pyramids-sheet 104 and totally-reflected by pyramid slope 105 as to be returned to the inside of housing 106 (i.e. to the side of light source 101).
Such returning light is reflected by reflection member 102 and incident to diffusion sheet 103 again, involving an attenuation of light (energy loss) due to repeated reflections between reflections member 102 and polygon-pyramids-sheet 104. Needless to say, this energy loss is not desirable.
According to the second prior art, much of the light obliquely incident to multiprism sheet 113 is emitted to a certain direction intensively from incident to multiprism sheet 113, then being deflected around the frontal direction by dark-area-removing sheet 114.
However, there are remarkable light components which are reflected by multiprism sheet 113, much of such reflected light being subject to repeated reflections between reflections member 112 and multiprism sheet 113. As a result, a remarkable energy loss is generated generally IN the same way as the first prior art.
In addition, the first prior art employs a combination of plural kinds of members including diffusion sheet 103 and polygon-pyramids-sheet 104. Similarly, the second prior art employs a combination of plural kinds of members including multiprism sheet 113 and dark-area-removing-sheet 114.
Therefore an increased numbers and kinds of members must be prepared, bringing much light loss at interfaces between the respective members and the exterior (air). Accordingly, it is difficult to satisfy demands for simplifying structure and reduction in number of part items.